The present invention relates to synthetic saturated oils, and their production and use. More particularly, it relates to novel synthetic saturated oils, their production from low molecular weight polyisoprene and compositions comprising them.
As lubricating oils, there are known petroleum lubricating oils, synthetic lubricating oils, fatty oils, etc. For the practical use, these oils are usually blended with various additives for improving their properties such as viscosity index improvers, flow point depressants, anti-corrosive agents and carbonization inhibitors. On lubricating oils used for the engines of jet planes, no lowering of physical properties between the two extremes of temperature is required. In case of lubricating oils for precision machines such as watches, a high viscosity index and a low flow point are considered as important. Automatic change gears also require high-quality lubricating oils. As lubricating oils meeting these requirements, there are proposed some synthetic oils. An example of them is oils obtained by polymerization of .alpha.-olefins using Lewis acid (e.g. aluminum chloride, aluminum bromide) as a catalyst. During the polymerization, however, isomerization takes place so as to change the branching of the polymers, thus giving no polymer having a high viscosity index. Another example is oils obtained by polymerization of .alpha.-olefins using a coordination anionic polymerization catalyst. These oils indicate usually a viscosity index of more than 130, a flash point of higher than 210.degree. C and a flow point of lower than -50.degree. C. However, with such flow point, they can not pass, for instance, the standards for hydraulic oils for airplanes under the American Military Standards (hereinafter referred to as "MIL") H-83282 and the standards for jet engine oils under MIL H-7807. In order to meet these standards, there is proposed a method for producing lubricating oils by polymerizing .alpha.-olefins having not less than 5 carbon atoms (e.g. octene-1, decene-1) in the presence of a catalyst composition comprising aluminum chloride and lithium aluminum hydride, followed by fractional distillation and hydrogenation. While the thus obtained saturated oils pass the said standards, there is still a demand to lubricating oils having a higher viscosity index.
On the other hand, there are known various synthetic oils for cosmetics such as liquid paraffin, glycerol and polyethylene glycol. However, these synthetic oils are inferior to squalene, which results from purification of shark oil, in penetration and absorption into the skin of human body. Squalene has the structure corresponding to the 1,4 polymerization product of isoprene, all the double bonds present therein having the trans configuration. Because of the presence of many double bonds, squalene is apt to be oxidized with air, whereby an offensive odor is generated and sometimes harmful substances to human body are produced. This drawback can be overcome by subjecting squalene to hydrogenation so as to make unsaturation degree of zero. The resulting hydrogenation product, i.e. squalene, is superior in weathering resistance and penetration into and non-toxicity to the skin of the human body. Since, however, squalene is a product isolated from sharks, it has become expensive with the reduction in the catch of sharks. Thus, the appearance of a synthetic oil comparable to squalene or squalene in various favorable properties in the use for cosmetics has been in high demand.
In order to provide synthetic oils suitable for various uses including lubricating oils and cosmetics, various attempts have been made up to the present time. Some of them are disclosed in Japanese Patent Publication (examined) No. 35,984/1974 Japanese Patent Publication (unexamined) Nos. 85,243/1974, 117,413/1974 and 133,302/1974, etc.
In Japanese Patent Publication (examined) No. 35,984/1974, the method comprises heat-polymerization of isoprene in the presence of a solid acid catalyst, and the isoprene may polymerize not in the straight form (i.e. 1,4 polymerization) but in the branched forms (e.g. cyclic polymerization, 3,4 polymerization, 1,2 polymerization). The polymerized isoprenes thus obtained have the structure in which an isopropenyl group, a vinyl group and a six-membered ring are linked to the side chains, and therefore they have a higher viscosity and a poorer flowing property than do the oils resulting from hydrogenation of natural straight terpenes.
In Japanese Patent Publication (unexamined) No. 85/243/1974, synthetic oils are produced by hydrogenation of low molecular weight polymers resulting from the polymerization of olefins having 4 carbon atoms such as isobutylene, butadiene and butene-1. The oils thus obtained have a high viscosity even if their molecular weight is low and are inferior to natural oils in flowing property.
Japanese Patent Publication (unexamined) Nos. 117,413/1974 and 133,302/1974 disclose a method wherein squalane is synthesized by coupling geranyl acetone and hexahydropseudoionone, followed by dehydration and hydrogenation. The produced oils have a flowing property close to that of natural squalene. However, this method is disadvantageous in requiring not only expensive starting materials (e.g. geranyl acetone and hexahydropseudoionone) but also many reaction stages (i.e. coupling, dehydration and hydrogenation).
As the result of an extensive study, it has now been found that hydrogenation of certain low molecular weight polyisoprene affords synthetic saturated oils, of which fractional distillation products have a wide variety of flow characteristics suitable for various uses including lubricating oils and cosmetics and some of them are quire similar to squalene in physical properties.
According to the present invention, synthetic saturated oils are produced by hydrogenation of low molecular weight polyisoprene having the 1,4 structure of at least 70% in the main chains and a number average molecular weight of about 150 to 3,000.
The starting material in the method of this invention is low molecular weight polyisoprene as defined above. When the 1,4 structure in the main chains is less than 70%, the resulting hydrogenation product can hardly flow or does not have a low viscosity. In general, the use of low molecular weight polyisoprene having a higher content of 1,4 structure affords a hydrogenation product of lower viscosity. Also, the use of the one having a higher content of cis structure gives a hydrogenation product of lower viscosity.
The low molecular weight polyisoprene suitable as the starting material may be produced by conventional procedures. For instance, such polyisoprene is obtainable by polymerization of isoprene in the presence of an .alpha.-olefin using a catalyst composition comprising an organometallic compound and a nickel compound with or without an electron donor as described in Japanese Patent Publication (unexamined) No. 115,189/1974. The molecular weight of the polymer to be produced can be readily regulated by controlling the amounts of the .alpha.-olefin, the organometallic compound, the nickel compound and the electron donor. Further, for instance, the suitable polyisoprene may be produced by living polymerization of isoprene by the use of a complex comprising metallic lithium and naphthalene in an inert solvent such as hexane as described in Journal of Polymer Science, 56, 449. Furthermore, for instance, the suitable polyisoprene may be produced by polymerization of isoprene using lithium salts as described in Japanese Patent Publication (unexamined) Nos. 35,102/1975, 46,606/1975 and 34,382/1975. Stillmore, for instance, the suitable polyisoprene may be produced by polymerization of isoprene in the presence of a radical initiator.
The low molecular weight polyisoprene thus produced may be separated as liquid polymer from the reaction mixture by a conventional separation procedure. For instance, the catalyst for polymerization is deactivated by treatment with methanol, ethanol, propanol, n-amyl alcohol, water or the like and then eliminated by washing with an aqueous solution of acid (e.g. hydrochloric acid, sulfuric acid, nitric acid, formic acid, acetic acid, oxalic acid). The resultant mixture is neutralized with an aqueous alkaline solution, washed with water and then concentrated under reduced pressure for removal of the solvent, whereby the liquid polymer is obtained.
Hydrogenation of the liquid polymer thus obtained may be carried out by treatment with hydrogen in the presence of a hydrogenation catalyst, usually at a temperature of about 50.degree. to 350.degree. C for about 1 to 100 hours under a hydrogen pressure of about 5 to 300 kg/cm.sup.2. The treatment may be carried out in the presence or absence of an inert solvent such as alcohols (e.g. methanol, ethanol), ketones (e.g. acetone, methylethylketone), aliphatic hydrocarbons (e.g. heptane, hexane, pentane, cyclohexane) or their mixtures. As the hydrogenation catalyst, there may be used any conventional one such as nickel (e.g. Raney nickel, nickel on diatomaceous earth, Urushibara nickel, palladium and platinum. After completion of the hydrogenation, the catalyst and the solvent are removed from the reaction mixture by usual methods, and the distillation of the reaction mixture under reduced pressure affords the hydrogenated product of the liquid polymer.
The thus obtained hydrogenated liquid polymer, i.e. the synthetic saturated oil of the invention, has a broad molecular weight distribution, comprises polymers ranging from low molecular weight ones to high molecular weight ones and shows generally the following physical properties:
Appearance: colorless, transparent, odorless;
Boiling point: B.P. (at 760 mmHg) .gtoreq. 150.degree. C;
Specific gravity: 0.79 .ltoreq. d.sup.20 .ltoreq. 0.92;
Refractive index: 1.40 .ltoreq. n.sub.D.sup.20 .ltoreq. 1.50;
Viscosity: 0.2 cp .ltoreq. .eta..sup.30.degree. C .ltoreq. 10.sup.5 cp.
The main components in such hydrogenated liquid polymer are hydrogenated polyisoprenes substantially representable by the formula: ##STR1## wherein R.sub.1 is hydrogen or alkyl having 1 to 8 carbon atoms, R.sub.2 is hydrogen, ethyl or isopropyl and n is an integer of 1 to 40. When, for instance, the hydrogenated liquid polymer is produced by hydrogenation of the liquid polymer according to the method described in Japanese Patent Publication (unexamined) No. 115,189/1974, its major components are the ones represented by the formula [I] wherein R.sub.1 is hydrogen and R.sub.2 is ethyl or isopropyl. Further, the hydrogenated liquid polymer produced by hydrogenation of a liquid polymer obtained by polymerization of isoprene in the presence of lithium or C.sub.1 -C.sub.8 alkyl lithium may comprise as its major components the ones represented by the formula [I] wherein R.sub.1 is hydrogen or C.sub.1 -C.sub.8 alkyl and R.sub.2 is hydrogen. Furthermore, for instance, the hydrogenated liquid polymer obtained by the process described in Example 2 as hereinafter presented contains as the major components the ones represented by the formula [I] wherein R.sub.1 is hydrogen and R.sub.2 is isopropyl and, when subjected to rectification and gel permeation chromatography, affords the following substances:
______________________________________ Boiling point Mole- Viscosity at 0.15 Specific Refractive cular at 25.degree. C Torr gravity, index n weight*) (cp) (.degree. C) d.sup.20 n.sub.D.sup.20 ______________________________________ 1 182 1.2 64 0.7931 1.4387 2 253 3.4 95 0.8003 1.4448 3 316 8.0 143 0.8051 1.4490 4 380 15.6 172 0.8092 1.4529 5 450 28 195 0.8125 1.4560 6 525 45 213 0.8160 1.4585 7-9 670 105 230-270 0.8208 1.4630 10-12 840 250 280-320 0.8263 1.4683 ______________________________________ Note: *)determined by the vapor pressure osmometry method
The hydrogenated liquid polymer may be separated by a conventional procedure such as fractional distillation into the initial fraction (30.degree. C .ltoreq. B.P./1 mmHg .ltoreq. 150.degree. C) having a low viscosity, the middle fraction (150.degree. C&lt;B.P./1 mmHg .ltoreq. 450.degree. C) having a medium viscosity and the residual matter (450.degree. C&lt;B.P./1 mmHg) having a high viscosity. These fractions are applied to various uses such as machine oils for precision machines (e.g. watches, measuring instruments, telephones), engine oils for automobiles and lubricating oils for jet planes and propeller planes depending on their viscosities and flash points. On these uses, they may be used alone or in combination with conventional additives such as viscosity index improvers, flow point depressants, anti-corrosive agents and carbonization inhibitors.
As well known, cosmetics are generally prepared by admixing together oil soluble materials such as vegetable oils (e.g. beeswax, vegitable wax, cetyl alcohol, stearic acid, lanolin, castor oil, olive oil), mineral oils (e.g. paraffin, liquid paraffin, vaseline, ceresine) and animal oils (e.g. squalane), water soluble material such as ethanol, glycerol, propylene glycol, polyethylene glycol, methyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, tragecanth gum and acacia gum, surfactants, coloring materials such as inorganic pigments (e.g. zinc stearate, ultramarine, titanium oxide, talc, kaolin), organic dyes and natural coloring matters, antioxidants, perfumes and water.
The hydrogenated liquid polymer obtained by this invention and the fractions therefrom may be used as oil soluble materials in the said cosmetics in the form of milky lotions, creams, stick pomades and the like. Since they are already hydrogenated, no deterioration in quality will be caused on those cosmetics.